Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$64.86	9.273%	$70.8745	$70.87	$70.85	$70.90
Purchase #2	$112.56	7.477%	$120.9761	$120.98	$121.00	$121.00
Purchase #3	$175.99	11.321%	$195.9138	$195.91	$195.90	$195.90
Purchase #4	$100.73	4.217%	$104.9778	$104.98	$105.00	$105.00
Purchase #5	$168.72	12.342%	$189.5434	$189.54	$189.55	$189.50
Purchase #6	$39.71	7.384%	$42.6422	$42.64	$42.65	$42.60
Purchase #7	$160.50	8.675%	$174.4234	$174.42	$174.40	$174.40
7 purchase totals =	$823.07		$899.3512	$899.34	$899.35	$899.30